The present invention relates to an apparatus for the automatic soldering of, for example, lead pins distributed in bilateral or quadrilateral parallel rows on a semiconductor chip, such as a packaged IC, with correspondingly distributed contact pins on a substrate plate of a printed circuit board, by heat irradiation. More particularly, the invention concerns an automatic soldering apparatus which produces at least a pair of parallel solder lines each emcompassing each of said bilateral or quadrilateral parallel rows of lead pins on a flat packaged IC, by exposing each of the lead pins to be soldered together with the contact pin pasted preliminarily with solder and aligned with said lead pin, to irradiation by a heat ray from a heat ray soldering head focussed as a line of focus in the form of a segment of a line corresponding to the soldering line, in such a manner that the adjustment and positioning of the lines of focus are effected automatically by the programmed control of mechanical actuation means that cause the heat ray soldering head to shift in the x- and/or y-coordinate direction and to turn the heat ray soldering head in the y- or x-coordinate direction on the substrate plate.
Conventional processing apparatus for mounting such a packaged IC on a substrate plate employs, for example, heating with a soldering iron, heating by a pulse heater, the so-called infrared heating reflow method, hot-air processes (Denshi-Zairyo, Materials for Electronics, 1985, No. 2, p. 37) and, as a recent proposal, laser beam heating (Keikinzoku-Yosetsu, Welding of Light Metals, Vol. 17, No. 1, 1979). These conventional techniques are accompanied by problems: for example, a small size IC package may often suffer from soldering failures, such as faulty alignment of the lead pins with the contact pins, shortcircuiting between the pins caused by excessive solder and so on, in particular when the lead pins of the IC package are densely distributed, especially for small size IC packages where the pitch or interval of the lead pins is quite small. Thus, a highly accurate printing of solder paste and a close control of work conditions, such as the mounting and positioning of the IC package on the substrate plate and so on, are required. On the other hand, due to the recent trend of employment of substrate materials of very low heat stability, such as paper, phenolic resin, etc., the substrate plate is apt to undergo thermal damage, especially when an infrared heating reflow technique, a hot-air process or laser beam heating is employed.
In the case of using laser beam heating, in which a laser beam is guided by a flexible light conduction fiber and the beam emission end thereof is moved to scan or track the soldering line by a beam scanning robot so as to focus the laser beam onto each contemplated coordinate point to effect the soldering, the beam emission head does not suffer from aging or time change by, for example, formation of a surface oxide layer etc., and thus, a stable soldering is attained, as contrasted with the case of heating by thermal conduction using for example a soldering iron etc. Here, however, an intensive irradiation by the laser beam occurs in the vicinity of the contemplated soldering spot by the diffraction of laser light, resulting in damage to the packaged IC and the substrate printed circuit board.
In particular, in the case of a packaged IC having quadrilateral rows of lead pins, there has never been proposed a processing technique in which the soldering in the directions of the x- and y-coordinates along the soldering lines is effected automatically by successive procedures.